Staggered in-situ deposition and etching of a dielectric layer for HDP CVD

ABSTRACT

A method for depositing a conformal dielectric layer employing a dep-etch technique features selectively decreasing the deposition gas present in a process chamber where a substrate to be covered by the conformal dielectric layer is disposed. By selectively decreasing the deposition gas present in the process chamber, the concentration of a sputtering gas, from which a plasma is formed, in the process chamber is increased. It is preferred that the flow of deposition gases be periodically terminated so as to provide a sputtering gas concentration approaching 100%. In this fashion, the etch rate of a conformal dielectric layer having adequate gap-filling characteristics may be greatly increased, while allowing an increase in the deposition rate of the same.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent appl. Ser. No.09/733,122, entitled “STAGGERED IN-SITU DEPOSITION AND ETCHING OF ADIELECTRIC LAYER FOR HDP-CVD,” filed Dec. 8, 2000 by Kent Rossman, nowU.S. Pat. No. 6,527,910, which is a divisional of U.S. patent appl. Ser.No. 09/045,278, entitled “STAGGERED IN-SITU DEPOSITION AND ETCHINGDIELECTRIC LAYER FOR HDP-CVD,” filed Mar. 20, 1998, now U.S. Pat. No.6,194,038, the entire disclosures of both of which are incorporatedherein by reference for all purposes.

BACKGROUND OF THE INVENTION

The present invention relates to the fabrication of integrated circuits.More particularly, the present invention is directed toward a method andapparatus for increasing the deposition rate of a conformal dielectriclayer, having excellent gap-filling characteristics, deposited over astepped surface.

Semiconductor device geometries continue to decrease in size, providingmore devices per unit area on a fabricated wafer. Currently, somedevices are fabricated with feature dimensions as small as 0.18 μm. Forexample, spacing between conductive lines or traces on a patterned wafermay be separated by 0.18 μm leaving recesses or gaps of a comparablesize. A nonconductive layer of dielectric material, such as silicondioxide, is typically deposited over the features to fill theaforementioned gap and insulate the features from other features of theintegrated circuit in adjacent layers or from adjacent features in thesame layer.

One problem encountered, as the feature dimensions of the integratedcircuits decrease, is that it becomes difficult to fill the gapscompletely between adjacent conductive lines. This problem is referredto as the gap-fill problem and is described below in conjunction withFIGS. 1 and 2. FIG. 1 shows a vertical cross-sectional view of asubstrate 10, such as a semiconductor wafer, having a layer ofconductive features 12, defining gaps, shown as 14. The sidewalls 16 ofthe gap are formed by one edge of adjacent conductive features 12.During deposition, dielectric material 18 accumulates on the surfaces 20of the conductive features 12, as well as the substrate 10 and formsoverhangs 22 located at the corners 24 of the conductive features 12. Asdeposition of the dielectric layer 16 continues, the overhangs 22typically grow together faster than the gap 14 is filled until adielectric layer 26 is formed, creating an interior void 28, shown moreclearly in FIG. 2. In this fashion, the dielectric layer 26 preventsdeposition into the interior void 28. The interior void 28 may beproblematic to device fabrication, operation, and reliability.

Many different techniques have been implemented to improve thegap-filling characteristics of dielectric layers, including depositionetch-back (dep-etch) techniques. One such dep-etch technique involvesphysical sputtering of the dielectric layer by ion bombardment toprevent the formation of voids during a deposition process. The effectsof the physical sputtering dep-etch technique is shown in FIG. 3. Asshown in FIG. 3, ions 30 incident on the dielectric material transferenergy thereto by collision, allowing atoms 32 to overcome local bindingforces and eject therefrom. During the dep-etch technique, dielectricmaterial fills the gap 14 forming a surface 34. The surface 34 lies in aplane that extends obliquely to the sidewalls 16, commonly referred toas a facet. This dep-etch technique may be applied sequentially so thatthe dielectric layer 26 is deposited and then subsequently etchedfollowed by deposition of additional dielectric material. Alternatively,the deposition process and the etch process may occur concurrently.Whether the deposition and etching are sequential or concurrent, thefirst order effects on the surface of the dielectric layer 26's profileare the same.

Referring to FIGS. 3 and 4, after an extended dep-etch technique, theportion of the dielectric layer 26 positioned adjacent to the corners24, regardless of the spacing between the conductive features 12, has asurface 34 that forms an oblique angle with respect to the plane inwhich the substrate 10 lies. Thereafter, planarization may beaccomplished by an extended planarization etch technique where physicalsputtering is balanced with the deposition so that very narrow featuresbecome completely planarized. Alternatively, a separate planarizationprocess may be employed that is capable of smoothing or eliminating theremaining steps of the large features.

Typically, a plasmachemical vapor deposition (CVD) process is employedto deposit a dielectric layer using the dep-etch technique. For example,a plasma-enhanced chemical vapor deposition (PECVD) process, or ahigh-density plasma-chemical vapor deposition process, such as anelectron cyclotron resonance chemical vapor deposition (ECR-CVD)process, may be employed. The plasma CVD processes typically allowdeposition of high quality films at lower temperature and with fasterdeposition rates than are typically possible employing purely thermallyactivated CVD processes. However, the deposition rates available usingconventional plasma CVD processes are still relatively low.

What is needed is a method and an apparatus for depositing a conformaldielectric layer over a stepped surface of a substrate at significantlyfaster rates than was previously possible in the prior art.

SUMMARY OF THE INVENTION

The present invention provides a method and apparatus for greatlyincreasing the deposition rate of a conformal dielectric layer employinga dep-etch technique. The invention does so by selectively increasinginert gas source concentration, in a process chamber, without asignificant increase in chamber pressure.

The dielectric layer is deposited employing a high-densityplasmachemical vapor deposition (HDP-CVD) system, such as an AppliedMaterials, Inc. Ultima HDP-CVD System. Typically, gaps having ahigh-aspect ratio of up to 2.5:1 may be present on a substrate uponwhich the dielectric layer is to be deposited, with the substrate beingpositioned in a process chamber of the HDP-CVD system. Deposition gases,such as a silicon source gas and an oxygen source gas are flowed acrossthe surface of the substrate along with an inert gas. An RF sourcegenerator and an RF bias generator are each in electrical communicationwith the process chamber to form a plasma from the process and inertgases.

An important consideration during the dep-etch technique is that thedeposition-to-etch ratio (dep-etch ratio) be maintained within apredetermined range so as to prevent over-etching and formation ofinterior voids. The present invention maintains the dep-etch ratiowithin a suitable range to prevent over-etch, while increasing thedeposition rate of the dielectric layer to provide a 100% gap-fill ofgaps having an aspect ratio up to 2.5:1. This is accomplished by rapidlyincreasing the etch rate of the dielectric layer, which allowsincreasing the deposition rate while maintaining a suitable dep-etchratio. Specifically, it was discovered that the etch-rate of adielectric layer is dependent not only upon the pressure of the processchamber, but also upon the concentration of the inert gas therein. Theetch rate was found to be inversely proportional to the pressure in theprocess chamber and proportional to the concentration of inert gaspresent therein. By selectively terminating the flow of deposition gasesin the process chamber, referred to as a staggered in-situ depositiontechnique, the pressure present therein may be decreased or maintained,while the inert gas concentration is substantially increased. In thisfashion, the etch rate of the dielectric layer is substantiallyincreased. The increased etch rate allows increasing the deposition rateusing any deposition technique known to those skilled in the art. Thisdecreases the time necessary to deposit the dielectric layer whilemaintaining a desired dep-etch ratio to provide the dielectric layerwith superior gap-filling characteristics.

In a preferred embodiment, the silicon source gas includes silane gas,SiH₄, and the oxygen source gas includes molecular oxygen gas, O₂. Theinert gas source is argon, Ar. The RF source generator operates at asource frequency of about 2 MHz and a source power level between about12-16 W/cm². The RF bias generator operates at a frequency of about13.56 MHz and a power level between about 7-13 W/cm². The processchamber pressure may be between about 2 and 10 millitorr, with 4-5millitorr being the preferred pressure range. To deposit the dielectriclayer, the silane, oxygen and argon gases are flowed into the processchamber. Specifically, silane is flowed into the process chamber at aflow rate in the range of 40-120 standard cubic centimeters per minutesccm. Oxygen is flowed into the process chamber at a flow rate in therange of 80-250 sccm, and argon is flowed into the process chamber at aflow rate in the range of 40-120 sccm. Selectively, during thedeposition process, either the silane flow, the oxygen flow or both arereduced so as to increase the concentration of argon flowing across thesubstrate. Typically, the flow of both silane and oxygen are terminatedfor approximately 1.5 seconds, during which time the concentration ofargon present in the process chamber is approximately 100%. During aprolonged dep-etch technique, the flow of either silane or oxygen, orboth gases are periodically reduced and/or terminated for apredetermined period of time. In this fashion, the etch rate may besubstantially increased to 6000 Å per minute, which allows an increasein the deposition rate to 10,000 Å per minute, while maintaining asuitable dep-etch ratio.

For a further understanding of the objects and advantages of the presentinvention, reference should be made to the ensuing detailed descriptiontaken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a vertical cross-sectional view of substrate, demonstratingaccumulation of dielectric material upon conductive features associatedtherewith, employing prior art deposition methods;

FIG. 2 is a vertical cross-sectional view of the substrate shown in FIG.1, demonstrating an interior void associated with prior art depositionmethods;

FIG. 3 is a vertical cross-sectional view of the substrate shown inFIGS. 1 and 2 in which a deposition-etch method is employed to removethe interior void shown in FIG. 2 in accordance with a prior art method;

FIG. 4 is a vertical, cross-sectional view of the substrate shown inFIGS. 1, 2 and 3 demonstrating the contour of a dielectric layerdisposed employing a prior art deposition etch method;

FIG. 5 is a simplified diagram of one embodiment of a HDP-CVD systemaccording to the present invention;

FIG. 6 is a simplified diagram of a monitor and light pen that may beused in conjunction with the exemplary CVD process chamber of FIG. 5;

FIG. 7 is a flow chart of an exemplary process control computer programproduct used to control the exemplary CVD process chamber of FIG. 5;

FIG. 8 is a cross-sectional view of an integrated circuit formedemploying the present invention;

FIG. 9 is a cross-sectional view of a substrate employed in the presentinvention;

FIG. 10 is a flow diagram of the method in accord with the presentinvention;

FIG. 11 is a cross-sectional view of the substrate shown in FIG. 10 witha gap-filling dielectric layer disposed thereon;

FIG. 12 is a graph showing the relationship between chamber pressure andetch rate of the dielectric layer shown in FIG. 11;

FIG. 13 is a graph showing the relationship between argon concentration,in a process chamber of the HDP-CVD system shown in FIG. 5 and etch rateof the dielectric layer shown in FIG. 12; and

FIG. 14 a flow diagram of an alternate embodiment of the method shownabove in FIG. 10.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

I. Introduction

In one embodiment, a conformal dielectric layer formed from silicondioxide is deposited on a stepped substrate employing a standard HDP-CVDsystem. A high deposition rate is achieved by selectively reducing theflow of deposition gases into a process chamber where a substrate havinga stepped surface to be covered by the conformal dielectric layer isdisposed. By selectively reducing the flow of deposition gases into theprocess chamber, the concentration of a sputtering gas, typicallycomprising argon, in the process chamber is increased without increasingthe pressure therein. In this fashion, the etch rate of the conformaldielectric layer, having superior gap-filling characteristics, may begreatly increased to allow an increase in the deposition rate of thesame, while maintaining a suitable dep-etch ratio.

II. An Exemplary CVD System

FIG. 5 illustrates one embodiment of a HDP-CVD system 36, in which adielectric layer according to the present invention can be deposited.The system 36 includes a process chamber 38, a vacuum system 40, asource plasma system 42, a bias plasma system 44, a gas delivery system46, and a remote plasma cleaning system 48.

An upper portion of process chamber 38 includes a dome 50, which is madeof a dielectric material, such as alumina or aluminum nitride. The dome50 defines an upper boundary of a plasma processing region 52. Theplasma processing region 52 is bounded on the bottom by the uppersurface of substrate 54 and the substrate support member 56.

A heater plate 58 and a cold plate 60 surmount, and are thermallycoupled to, the dome 50. The heater plate 58 and the cold plate 60 allowcontrol of the dome temperature to within about ±10° C. over a range ofabout 100° C. to 200° C. This allows optimizing the dome temperature forthe various processes. For example, it may be desirable to maintain thedome at a higher temperature for cleaning or etching processes than fordeposition processes. Accurate control of the dome temperature alsoreduces the flake or particle counts in the process chamber and improvesadhesion between the deposited layer and the substrate.

The lower portion of process chamber 38 includes a body member 62, whichjoins the process chamber to the vacuum system. A base portion 64 of thesubstrate support member 56 is mounted on, and forms a continuous innersurface with, body member 62. Substrates are transferred into and out ofprocess chamber 38 by a robot blade (not shown) through aninsertion/removal opening 95 in the side of process chamber 38. A motor(not shown) raises and lowers a lift-pin plate (not shown) that raisesand lowers lift pins (not shown) that raise and lower the wafer. Upontransfer into process chamber 38, substrates are loaded onto the raisedlift pins, and then lowered to a substrate receiving portion 66 ofsubstrate support member 56. Substrate receiving portion 66 includes anelectrostatic chuck 68 that secures the substrate to substrate supportmember 56 during substrate processing.

The vacuum system 40 includes a throttle body 70, which housestwin-blade throttle valve 72 and is attached to gate valve 74 andturbomolecular pump 76. It should be noted that throttle body 70 offersminimum obstruction to gas flow, and allows symmetric pumping, asdescribed in co-pending, co-assigned U.S. patent application, originallyfiled on filed Dec. 12, 1995, and assigned Ser. No. 08/574,839, refiledon Sep. 11, 1996 and assigned Ser. No. 08/712,724 entitled “SYMMETRICCHAMBER”. The gate valve 74 can isolate the pump 76 from the throttlebody 70, and can also control process chamber pressure by restrictingthe exhaust flow capacity when throttle valve 72 is fully open. Thearrangement of the throttle valve 72, gate valve 74, and turbo molecularpump 76 allow accurate and stable control of process chamber pressuresfrom about 1 to 100 millitorr.

The source plasma system 42 includes a top coil 78 and side coil 80,mounted on dome 50. A symmetrical ground shield (not shown) reduceselectrical coupling between the coils. Top coil 78 is powered by top RFsource generator 82, while the side coil 80 is powered by side RF sourcegenerator 84, allowing independent power levels and frequencies ofoperation for each coil. This dual coil system allows control of theradial ion density in process chamber 38, thereby improving plasmauniformity. Side coil 80 and top coil 78 couple energy into the chamber38 inductively. In a specific embodiment, the top RF source generator 82provides up to 2500 W of RF power at nominally 2 MHz and the side RFsource generator 84 provides up to 5000 W of RF power at nominally 2MHz. The operating frequencies of the top and side RF generators may beoffset from the nominal operating frequency (e.g., to 1.7-1.9 MHz and1.9-2.1 MHz, respectively) to improve plasma-generation efficiency.

The RF generators 82 and 84 include digitally controlled synthesizersand operate over a frequency range from about 1.7 to about 2.1 MHz. Eachgenerator includes an RF control circuit (not shown) that measuresreflected power from the process chamber and coil back to the generator,and adjusts the frequency of operation to obtain the lowest reflectedpower, as understood by a person of ordinary skill in the art. RFgenerators are typically designed to operate into a load with acharacteristic impedance of 50 Ω. RF power may be reflected from loadsthat have a different characteristic impedance than the generator. Thiscan reduce power transferred to the load. Additionally, power reflectedfrom the load back to the generator may overload and damage thegenerator. Because the impedance of a plasma may range from less than 5Ω to over 900 Ω, depending on the plasma ion density among otherfactors, and because reflected power may be a function of frequency,adjusting the generator frequency according to the reflected powerincreases the power transferred from the RF generator to the plasma andprotects the generator. Another way to reduce reflected power andimprove efficiency is with a matching network.

Matching networks 89 and 90 match the output impedance of generators 82and 84 with coils 78 and 80, respectively. The RF control circuit maytune both matching networks by changing the value of capacitors withinthe matching networks to match the generator to the load as the loadchanges. The RF control circuit may tune a matching network when thepower reflected from the load back to the generator exceeds a certainlimit. One way to provide a constant match, and effectively disable theRF control circuit from tuning the matching network, is to set thereflected power limit above any expected value of reflected power. Thismay help stabilize a plasma under some conditions by holding thematching network constant at its most recent condition.

The bias plasma system 44 includes a RF bias generator 86 and a biasmatching network 88. The bias plasma system 44 capacitively couplessubstrate receiving portion 66 to the body member 62, which act ascomplementary electrodes. The bias plasma system 44 serves to enhancethe transport of plasma species created by the source plasma system 42to the surface of the substrate. In a specific embodiment, the RF biasgenerator 86 provides up to 5000 W of RF power at 13.56 MHz.

Other measures may also help stabilize a plasma. For example, the RFcontrol circuit can be used to determine the power delivered to the load(plasma) and may increase or decrease the generator output power to keepthe delivered power substantially constant during deposition of a layer.

The gas delivery system 46 includes a plurality of gas sources 100 a,100 b, 100 c, 100 d and 100 e. In one embodiment, the aforementioned gassources comprise of silane, molecular oxygen, silicon fluoride andargon, respectively. The gas deliverly system 46 provides gases fromseveral sources to the process chamber for processing the substrate viagas delivery lines 92 (only some of which are shown). Gases areintroduced into the process chamber 38 through a gas ring 94, a topnozzle 96, and a top vent 98. Specifically, gas sources, 100 a and 100d, provide gas to top nozzle 96 via flow controllers 120 a and 120 c,respectively, and gas delivery lines 92. Gas from gas source 100 b isprovided to gas vent 98 via flow controller 120 b. The top nozzle 96 andtop vent 98 allow independent control of top and side flows of thegases, which improves film uniformity and allows fine adjustment of thefilm's deposition and doping parameters. The top vent 98 is an annularopening around the top nozzle 96 through which gas may flow into theprocess chamber from the gas delivery system.

Gas is provided from each of the aforementioned gas sources to gas ring94 via flow controller 102 a, 102 b, 102 c, 102 d and 102 e and gasdelivery lines 92. Gas ring 94 has a plurality of gas nozzles 106 and108 (only two of which is shown) that provide a uniform flow of gas overthe substrate. Nozzle length and nozzle angle may be changed by changinggas ring 94. This allows tailoring the uniformity profile and gasutilization efficiency for a particular process within an individualprocess chamber. In a specific embodiment, the gas ring 94 has a totalof twenty-four gas nozzles, twelve first gas nozzles 108 and twelvesecond gas nozzles 106. Typically, gas nozzles 108 (only one of which isshown), are coplanar with, and shorter than, the second gas nozzles 106.

In some embodiments, flammable, toxic, or corrosive gases may be used.In these instances, it may be desirable to eliminate gas remaining inthe gas delivery lines after a deposition. This may be accomplishedusing a three-way valve, such as valve 112, to isolate process chamber38 from delivery line 92 a, and to vent delivery line 92 a to vacuumforeline 114, for example. As shown in FIG. 5, other similar valves,such as 112 a and 112 b, may be incorporated on other gas deliverylines. Such three-way valves may be placed as close to process chamber38 as practical, to minimize the volume of the unvented gas deliveryline (between the three-way valve and the process chamber).Additionally, two-way (on-off) valves (not shown) may be placed betweena mass flow controller (MFC) and the process chamber or between a gassource and an MFC.

The remote microwave-generated plasma cleaning system 48 is provided toperiodically clean deposition residues from process chamber components.The cleaning system includes a remote microwave generator 124 thatcreates a plasma from a cleaning gas source 100 e, such as fluorine,nitrogen trifluoride, or equivalents, in reactor cavity 126. Thereactive species resulting from this plasma are conveyed to processchamber 38 through cleaning gas feed port 128 via applicator tube 130.The materials used to contain the cleaning plasma (e.g., cavity 126 andapplicator tube 130) should be resistant to attack by the plasma. Thedistance between reactor cavity 126 and feed port 128 should be kept asshort as practical, as the concentration of desirable plasma species maydecline with distance from reactor cavity 126. Generating the cleaningplasma in a remote cavity allows the use of an efficient microwavegenerator and does not subject process chamber components to thetemperature, radiation, or bombardment of the glow discharge that may bepresent in an in situ plasma. Consequently, relatively sensitivecomponents, such as the electrostatic chuck 68, do not need to becovered with a dummy wafer or otherwise protected, as may be requiredwith an in situ plasma cleaning process. During the cleaning process, orother processes, the gate valve 74 may be closed to isolate theturbomolecular vacuum pump 76 from the process chamber. In thisconfiguration, the foreline 114 provides a process vacuum generated byremote vacuum pumps, which are typically mechanical vacuum pumps.Isolating the turbomolecular pump from the process chamber with the gatevalve protects the turbomolecular pump from corrosive compounds or otherpotentially harmful effects resulting from the process chamber clean orother processes.

A system controller 132 regulates the operation of system 36 andincludes a processor 134 in electrical communication therewith toregulate the operations thereof. Typically, the processor 134 is part ofa single-board computer (SBC), that includes analog and digitalinput/output boards, interface boards and stepper motor controllerboards. Various components of the CVD system 36 conform to the VersaModular European (VME) standard, which defines board, card cage, as wellas connector type and dimensions. The VME standard also defines the busstructure as having a 16-bit data bus and a 24-bit address bus. Theprocessor 134 executes system control software, which is a computerprogram stored in a memory 136, electronically coupled to the processor134. Any type of memory device may be employed, such as a hard diskdrive, a floppy disk drive, a card rack or a combination thereof. Thesystem control software includes sets of instructions that dictate thetiming, mixture of gases, process chamber pressure, process chambertemperature, microwave power levels, pedestal position, and otherparameters of a particular process, discussed more fully below withrespect to FIG. 7.

Referring to FIG. 6, the interface between a user and the processor 134is via a CRT monitor 138 and light pen 140 In the preferred embodimenttwo monitors 138 and 138′ are used, each having a light pen associatedtherewith, 140 and 140′, respectively. One of the monitors 138 ismounted in a clean room wall 144 for the operators and the other behindthe wall for the service technicians. The CRT monitors 138 and 138′ maysimultaneously display the same information, but only one of the lightpens 140 and 140′ is enabled for data input during any given time. Werelight pen 140 employed to communicate with the processor 134, anoperator would place the same on the screen of the CRT monitor 138. Alight sensor (not shown) located at the tip of the light pen 140 detectslight emitted by the CRT monitor 138. To select a particular screen orfunction, the operator touches a designated area of the CRT monitor 138and pushes a button (not shown) on the light pen 140. The touched areaprovides a visual response, such as a change in color, or a new menu orscreen being displayed, confirming communication between the light pen140 and the CRT monitor 138. Other input devices, such as a keyboard,mouse, or other pointing or communication device, may be used instead ofor in addition to the light pen 140 to allow the user to communicatewith the processor 134.

The process for depositing the film can be implemented using a computerprogram product that is executed by the processor 134. The computerprogram code can be written in any conventional computer readableprogramming language, for example, 68000 assembly language, C, C++,Pascal, Fortran or others. Suitable program code is entered into asingle file, or multiple files, using a conventional text editor, andstored or embodied in a computer usable medium, such as the memory 136,shown in FIG. 5. If the entered code text is in a high level language,the code is compiled, and the resultant compiler code is then linkedwith an object code of precompiled Windows™ library routines. To executethe linked, compiled object code the system user invokes the objectcode, causing the processor 134 to load the code in the memory 136. Theprocessor 134 then reads and executes the code to perform the tasksidentified in the program.

FIG. 7 shows an illustrative block diagram of the hierarchical controlstructure of system control software 146. A user enters a process setnumber and process chamber number into a process selector subroutine 148in response to menus or screens displayed on the CRT monitor by usingthe light pen interface. The process sets are predetermined sets ofprocess parameters necessary to carry out specified processes, and areidentified by predefined set numbers. Process selector subroutine 148identifies (i) the desired process chamber in a multichamber system, and(ii) the desired set of process parameters needed to operate the processchamber for performing the desired process. The process parameters forperforming a specific process relate to process conditions such as, forexample, process gas composition and flow rates, temperature, pressure,plasma conditions such as RF power levels, and process chamber dometemperature, and are provided to the user in the form of a recipe. Theparameters specified by the recipe are entered utilizing the lightpen/CRT monitor interface.

The signals for monitoring the process are provided by the analog inputand digital input boards of the system controller and the signals forcontrolling the process are output on the analog output and digitaloutput boards of the system controller.

A process sequencer subroutine 150 comprises program code for acceptingthe identified process chamber and set of process parameters from theprocess selector subroutine 148, and for controlling operation of thevarious process chambers. Multiple users can enter process set numbersand process chamber numbers, or a user can enter multiple process setnumbers and process chamber numbers, so sequencer subroutine 150operates to schedule the selected processes in the desired sequence.Preferably, sequencer subroutine 150 includes a program code to performthe steps of (i) monitoring the operation of the process chambers todetermine if the process chambers are being used, (ii) determining whatprocesses are being carried out in the process chambers being used, and(iii) executing the desired process based on availability of a processchamber and type of process to be carried out. Conventional methods ofmonitoring the process chambers can be used, such as polling. Whenscheduling which process is to be executed, sequencer subroutine 150 canbe designed to take into consideration the present condition of theprocess chamber being used in comparison with the desired processconditions for a selected process, or the “age” of each particular userentered request, or any other relevant factor a system programmerdesires to include for determining scheduling priorities.

After sequencer subroutine 150 determines which process chamber andprocess set combination is going to be executed next, sequencersubroutine 150 causes execution of the process set by passing theparticular process set parameters to process chamber manager subroutines152, 154 and 156, which control multiple processing tasks in processchamber 38 and possibly other process chambers (not shown) according tothe process set determined by sequencer subroutine 150.

Examples of process chamber component subroutines are substratepositioning subroutine 158, process gas control subroutine 160, pressurecontrol subroutine 162, and plasma control subroutine 164. Those havingordinary skill in the art will recognize that other process chambercontrol subroutines can be included depending on what processes aredesired to be performed in process chamber 38. In operation, processchamber manager subroutine 152 selectively schedules or calls theprocess component subroutines in accordance with the particular processset being executed. Scheduling by process chamber manager subroutine 152is performed in a manner similar to that used by sequencer subroutine150 in scheduling which process chamber and process set to execute.Typically, process chamber manager subroutine 152 includes steps ofmonitoring the various process chamber components, determining whichcomponents need to be operated based on the process parameters for theprocess set to be executed, and causing execution of a process chambercomponent subroutine responsive to the monitoring and determining steps.

Referring to both FIGS. 5 and 7, in operation the substrate positioningsubroutine 158 comprises program code for controlling process chambercomponents that are used to load the substrate 54 onto substrate supportnumber 68. The substrate positioning subroutine 158 may also controltransfer of a substrate into process chamber 38 from, e.g., a PECVDreactor or other reactor in the multichamber system, after otherprocessing has been completed.

The process gas control subroutine 160 has program code for controllingprocess gas composition and flow rates. Subroutine 160 controls theopen/close position of the safety shut-off valves, and also rampsup/down the mass flow controllers to obtain the desired gas flow rates.All process chamber component subroutines, including process gas controlsubroutine 160, are invoked by process chamber manager subroutine 152.Subroutine 160 receives process parameters from process chamber managersubroutine 152 related to the desired gas flow rates.

Typically, process gas control subroutine 160 operates by opening thegas supply lines, and repeatedly (i) reading the necessary mass flowcontrollers, (ii) comparing the readings to the desired flow ratesreceived from process chamber manager subroutine 152, and (iii)adjusting the flow rates of the gas supply lines as necessary.Furthermore, process gas control subroutine 160 may include steps formonitoring the gas flow rates for unsafe rates, and activating thesafety shut-off valves when an unsafe condition is detected.

In some processes, an inert gas, such as argon, is flowed into processchamber 13 to stabilize the pressure in the process chamber beforereactive process gases are introduced into the process chamber. Forthese processes, the process gas control subroutine 160 is programmed toinclude steps for flowing the inert gas into process chamber 38 for anamount of time necessary to stabilize the pressure in the processchamber. The above-described steps may then be carried out.

Additionally, when a process gas is to be vaporized from a liquidprecursor, for example, tetraethoxysilane (TEOS), the process gascontrol subroutine 160 may include steps for bubbling a delivery gassuch as helium through the liquid precursor in a bubbler assembly or forintroducing the helium to a liquid injection valve. For this type ofprocess, the process gas control subroutine 160 regulates the flow ofthe delivery gas, the pressure in the bubbler, and the bubblertemperature to obtain the desired process gas flow rates. As discussedabove, the desired process gas flow rates are transferred to process gascontrol subroutine 160 as process parameters.

Furthermore, the process gas control subroutine 160 includes steps forobtaining the necessary delivery gas flow rate, bubbler pressure, andbubbler temperature for the desired process gas flow rate by accessing astored table containing the necessary values for a given process gasflow rate. Once the necessary values are obtained, the delivery gas flowrate, bubbler pressure and bubbler temperature are monitored, comparedwith the necessary values and adjusted accordingly.

The process gas control subroutine 160 may also control the flow ofheat-transfer gas, such as helium (He), through the inner and outerpassages in the wafer chuck with an independent helium control (IHC)subroutine (not shown). The gas flow thermally couples the substrate tothe chuck. In a typical process, the wafer is heated by the plasma andthe chemical reactions that form the layer, and the He cools thesubstrate through the chuck, which may be watercooled. This keeps thesubstrate below a temperature that may damage preexisting features onthe substrate.

Pressure control subroutine 162 includes program code for controllingthe pressure in process chamber 38 by regulating the size of the openingof throttle valve 72 in the exhaust portion of the process chamber.There are at least two basic methods of controlling the process chamberwith the throttle valve. The first method relies on characterizing theprocess chamber pressure as it relates to, among other things, the totalprocess gas flow, size of the process chamber, and pumping capacity. Thefirst method sets throttle valve 72 to a fixed position. Settingthrottle valve 72 to a fixed position may eventually result in asteady-state pressure.

Alternatively, the process chamber pressure may be measured with amanometer, for example, and throttle valve 72 position may be adjustedaccording to pressure control subroutine 162, assuming the control pointis within the boundaries set by gas flows and exhaust capacity. Theformer method may result in quicker process chamber pressure changes, asthe measurements, comparisons, and calculations associated with thelatter method are not invoked. The former method may be desirable whenprecise control of the process chamber pressure is not required, whereasthe latter method may be desirable when an accurate, repeatable, andstable pressure is desired, such as during the deposition of a layer.

When pressure control subroutine 162 is invoked, the desired (or target)pressure level is received as a parameter from process chamber managersubroutine 152. Pressure control subroutine 162 operates to measure thepressure in process chamber 38 by reading one or more conventionalpressure manometers connected to the process chamber, compare themeasure value(s) with the target pressure, obtain proportional,integral, and differential (PID) values from a stored pressure tablecorresponding to the target pressure, and adjust throttle valve 72according to the PID values obtained from the pressure table.Alternatively, pressure control subroutine 162 may open or closethrottle valve 72 to a particular opening size to regulate the pressurein process chamber 38 to a desired pressure or pressure range.

The plasma control subroutine 164 comprises program code for controllingthe frequency and power output setting of RF generators 82 and 84, andfor tuning matching networks 88 and 90. Plasma control subroutine 164,like the previously described process chamber component subroutines, isinvoked by process chamber manager subroutine 152.

An example of a system which may incorporate some or all of thesubsystems and routines described above would be an Ultima System,manufactured by Applied Materials, configured to practice the presentinvention.

III. Exemplary Structure

FIG. 8 illustrates a simplified cross-sectional view of an integratedcircuit 166 incorporating features of the present invention. As shown inFIG. 8, integrated circuit 166 includes NMOS and PMOS transistors 168and 170, which are separated and electrically isolated from each otherby a field oxide region 172. Each transistor 168 and 170 comprises asource region 174, a gate region 176, and a drain region 178.

A premetal dielectric layer 180 separates transistors 168 and 170 from ametal layer 182, with connections between metal layer 182 and thetransistors made by contacts 184. The metal layer 182 is one of fourmetal layers, 182, 186, 188 and 190, included in integrated circuit 166.Each metal layer 182, 186, 188 and 190 is separated from adjacent metallayers by respective intermetal dielectric layers 192, 194 and 196, andmay be formed by processing steps such as aluminum deposition andpatterning. Adjacent metal layers are connected at selected openings byvias 198. Deposited over metal layer 190 are planarized passivationlayers 200.

Embodiments of the present invention are particularly useful forintermetal dielectric (IMD) layers, but may find uses in each of thedielectric layers shown in integrated circuit 166. The simplifiedintegrated circuit 166 is for illustrative purposes only. One ofordinary skill in the art could implement the present method forfabrication of other integrated circuits such as microprocessors,application-specific integrated circuits (ASICs), memory-devices, andthe like. Additionally, the method of the present invention may be usedin the fabrication of integrated circuits using other technologies suchas BiCMOS, NMOS, bipolar and others.

IV. Staggered In-situ Deposition

Referring to both FIGS. 5 and 9, the method of the present invention maybe employed to deposit dielectric layers on the substrate 56 positionedin the (HDP-CVD) system 36. Although the substrate may have virtuallyany topography, the substrate 54 typically has stepped surfaces and withhave one or more film layers disposed thereon, shown as 202 and 204. Thefilm layer 202 is typically formed from a conductive material that hasone or more vias 206 formed therein, before deposition of a dielectriclayer employing the present invention. The via 206 may have an aspectratio of up to 2.5:1 or more, with the aspect ratio being defined as theheight of the via 206, H, divided by the via 206's width, W.

Referring to FIGS. 5, 9 and 10, the method includes a step 208 duringwhich the substrate 54 is positioned in the process chamber 38 proximateto the plasma processing region 52. Subsequent to step 208, an inert gasis flowed into the process chamber 38, during step 210. After the inertgas is introduced into the process chamber 38, a plasma is struck atstep 212. Following step 212, a deposition gas is introduced into theprocess chamber 38, at step 214. The aforementioned inert gas typicallycomprises a flow of argon gas, Ar. The deposition gas consists of, forexample, a silicon source gas, such as silane gas, Si₄, and an oxygensource gas, such as molecular oxygen gas, O₂. During the step 210, it ispreferred that flow rate of argon is in the range of 40-120 sccm. Theflow rate of the silane gas is in the range of 40-120 sccm, and theoxygen gas is flowed into the process chamber at a flow rate in therange of 80-250 sccm. The aforementioned plasma is formed by the RFsource generators 82 and 84 creating an RF field in the plasmaprocessing region 52 having a frequency of about 2 MHz and a power levelbetween about 12-16 W/cm², and the RF bias generator 86 creating an RFfield having a frequency of about 13.56 MHz and a power level betweenabout 7-13 W/cm². Typically, the pressure in the process chamber ismaintained between about 2 and 10 millitorr, with 4-5 millitorr beingthe preferred pressure range. During step 214, the dielectric layer 215,is deposited over layers 202 and 204 to fill the gap 206 (shown in FIG.10) and is concurrently, which is understood to be primarily attributedto the ions generated from the argon gas. The source components of theplasma dissociates the atoms and molecules of the process chamber gasesinto a plasma, and the bias component of the plasma moves the plasmaspecies to and from the surface of the dielectric layer being deposited.The bias component conveys deposition ions to the dielectric layersurface for combination therein and sputtering thereof.

An important consideration when depositing the dielectric layer 214using a dep-etch technique is maintaining a suitable dep-etch ratio toprevent over etching of the dielectric layer 215 and formation ofinterior voids. For purposes of this application, the dep etch-ratio isdefined as follows:

 D/E=D _(S) /[D _(S) −D _((S+B))]

where D/E is the dep-etch ratio, D_(S) is the deposition rate with onlythe RF source applied, and D_((S+B)) is the deposition rate with boththe RF source and the RF bias applied. The range advocated for thedep-etch ratio is typically dependent upon the largest aspect ratiopresent on the substrate surface. It has been found that with a 2.5:1aspect ratio, the dep-etch ratio should be kept within the range of2.8:1 to 3.2:1. In accordance with this finding, a dep-etch ratio lessthan 2.8:1 may result in over-etching of the step surface, and adep-etch ratio in excess of 3.2:1 may result in the formation ofinterior voids.

The dep-etch ratio may be varied in a number of ways. For example, thedep-etch ratio may be increased by either increasing the deposition rateat a substantially constant etch rate, or decreasing the etch rate at asubstantially constant deposition rate both results in an increaseddep-etch ratio. Conversely, the dep-etch ratio may be decreased bydecreasing the deposition rate at a substantially constant etch rate, orby increasing the etch rate at a substantially constant deposition rate.Varying the RF bias energy also affects the dep-etch ratio.Specifically, it is believed that by decreasing the RF bias energy, theetch-rate is decreased and the deposition rate is increased, therebyincreasing the dep-etch ratio. By increasing the RF bias energy, thedep-etch ratio may be decreased in an analogous manner. However, it isnot preferred to vary the RF bias energy, because the same is optimizedto obtain plasma uniformity. Varying the RF bias energy could degradeplasma uniformity, which could degrade the quality of a depositeddielectric layer.

Referring to both FIGS. 10 and 11, the present method allows asubstantial increase in both the deposition rate and the etch rate whilemaintaining a suitable dep-etch ratio and without affecting plasmauniformity, i.e., without changing the RF bias energy. The method doesso by selectively reducing the flow into the process chamber 38, ofeither the silane source or the oxygen source, or both, at step 216. Inthis fashion, the present method takes advantage of a discovery that theetch rate of the dielectric layer 215 is dependent not only upon thepressure of the process chamber, but also upon the concentration of theinert gas therein. Specifically, it was found that, for a given RF biaspower, the etch rate is inversely proportional to the pressure in theprocess chamber and proportional to the concentration of inert gaspresent therein. For example, the curve 218, shown in FIG. 12, showsthat at a chamber pressure of 60 millitorr, the etch rate of adielectric layer is less than 200 Å per minute. A chamber pressure of 10millitorr, on the other hand, provides an etch rate for a dielectriclayer in excess of 600 Å per minute, a three-fold increase. As shown bythe curve 220 in FIG. 13, the argon concentration in the process chamber38 also effects the etch rate. As shown, by the curve 220, at an argonconcentration level in the range of 20% to 80% there is a negligiblechange in the etch rate of the dielectric layer. However, at argon gasconcentration levels reaching 100%, the etch rate of the dielectriclayer is greatly increased, reaching nearly 1,200 Å per minute. Thisallows increasing the deposition rate using any suitable means known tothose skilled in the art, e.g., increasing the flow rate of thedeposition gases, while maintaining a suitable dep-etch ratio. Ifpreferred, the deposition rate may be greatly increased, employing thepresent invention, while maintaining a constant dep-etch ratio.

Referring to FIGS. 5, 10 and 11 to take advantage of the aforementionedconcepts, it was discovered that the etch rate of the dielectric layermay be greatly increased by selectively decreasing the flow ofdeposition gases into the process chamber 38. In this fashion, thepressure present therein may be decreased or maintained, while the inertgas concentration is substantially increased. Increasing the etch rate,as discussed above, allows increasing the flow rate of the depositiongases into the process chamber 38, thereby increasing the depositionrate while maintaining a desired dep-etch ratio. This decreases the timenecessary to deposit the dielectric film, while maintaining superior gapfilling characteristics of the dielectric film. To that end, after theplasma is struck at 212, the silicon source and oxygen source gases areflowed into the process chamber 38 for a predetermined amount of time,as step 214, which is dependent upon both the plasma species present andthe desired thickness of the resulting dielectric layer. For example,with the aforementioned plasma, a dielectric layer having a thicknessapproximating 10,000 Å may be formed within 90 to 120 seconds.

In a preferred embodiment, step 216 occurs approximately 60-70 secondsafter step 214. During step 216 the flow of both the silicon source gasand the oxygen source gas are simultaneously terminated forapproximately 10-15 seconds, allowing the concentration of argon presentin the process chamber 38 to approach 100%. Thereafter, shown as step222, the silicon source gas and the oxygen source gas are again flowedinto the process chamber 38 at the rate described above with respect tostep 210. The flow rate of the silicon and oxygen source gases may beperiodically reduced, during a prolonged dep-etch technique, byrepeating steps 216 and 222, shown as step 224. In this fashion, theetch rate of the dielectric layer 215 may be substantially increased,while maintaining a suitable deposition-to-etch ratio (dep-etch ratio).With the method described above, the etch rate at step 216 may be up to6,000 Å per minute or more. This allows an increase in the depositionrate, at steps 214 and 222, in excess of 10,000 Å per minute.

As mentioned above, an increased etch rate of the dielectric layer 215may be obtained by merely decreasing the flow of one of the silane gasor oxygen gas. As a result, the method, shown in FIG. 14 may be employedfor depositing a dielectric layer. Step 308 is identical to step 208,described above in FIG. 10. Step 310 of FIG. 14, however, includesflowing both an inert gas and an oxygen source gas into the processchamber 38, shown in FIG. 5. At step 312, a plasma is formed therein, asdiscussed above, with respect to step 212 and shown in FIG. 11.Thereafter, at step 314 shown in FIG. 14, the silane source gas isflowed into the process chamber 38, shown in FIG. 5. At step 316, theflow of silane is decreased so as to achieve a desired etch rate of thedielectric layer being deposited. At step 322, the flow of the silanegas source is restarted to the flow rate of the silane gas source atstep 314. The flow rate of the silicon source gas may be periodicallyreduced, during a prolonged dep-etch technique, by repeating steps 316and 322, shown as step 324 to obtain a dielectric layer of desiredthickness. The method may be varied to control both the deposition andetch rates as desired. The scope of the invention should, therefore, bedetermined not with reference to the above description, but insteadshould be determined with reference to the appended claims along withtheir full scope of equivalents.

What is claimed is:
 1. A method for depositing a conformal dielectriclayer on a substrate disposed in a substrate processing chamber, themethod comprising: flowing, into the chamber, a deposition gas and aninert gas source; forming a high density plasma in the chamber todeposit the conformal layer over the substrate; and during deposition ofthe conformal dielectric layer, selectively decreasing the depositiongas present in the process chamber thereby decreasing a relativeconcentration of the deposition gas to the inert gas.
 2. The method ofclaim 1 further comprising, after the step of selectively decreasing thedeposition gas and during deposition of the conformal dielectric layer,selectively increasing the deposition gas present in the process chamberthereby increasing a relative concentration of the deposition gas to theinert gas.
 3. The method of claim 2 wherein the deposition gas comprisesa silicon source and an oxygen source.
 4. The method of claim 3 whereinthe step of selectively decreasing the deposition gas includes excludingthe deposition gas from the chamber for a predetermined period of time.5. The method of claim 3 wherein the inert gas source comprises argon.6. The method of claim 3 wherein the conformal dielectric layer isdeposited over a gap formed between adjacent raised surfaces, the gaphaving an aspect ratio of 2.5:1 or higher.
 7. The method of claim 6wherein the silicon source is silane (SiH₄) and the oxygen source ismolecular oxygen (O₂).
 8. The method of claim 2 further comprising,after the step of selectively increasing the deposition gas and duringdeposition of the conformal layer, repeating one or more times asequence of (i) decreasing a relative concentration of the depositiongas to the inert gas and then (ii) increasing the relative concentrationof the deposition gas to the inert gas.
 9. The method of claim 1 whereinforming the high density plasma comprises forming an inductively coupledhigh density plasma.
 10. A method for depositing a dielectric layer overa substrate disposed in a substrate processing chamber, the methodcomprising: depositing a first portion of the dielectric layer over thesubstrate using a high density plasma process having a firstdeposition-to-etch ratio; thereafter, decreasing the firstdeposition-to-etch ratio of the high density plasma process to a seconddeposition-to-etch ratio while maintaining a high density plasma in thesubstrate processing chamber; and thereafter, depositing a secondportion of the dielectric layer over the substrate by increasing thesecond deposition-to-etch ratio of the high density plasma process to athird deposition-to-etch ratio while maintaining a high density plasmain the substrate processing chamber.
 11. The method of claim 9, whereinthe step of depositing a first portion of the dielectric layer comprisesforming a high density plasma from a deposition gas and an inert gas.12. The method of claim 11 wherein the step of decreasing the firstdeposition-to-etch ratio to a second deposition-to-etch ratio comprisesdecreasing a concentration of the deposition gas relative to aconcentration of the inert gas.
 13. The method of claim 12 wherein thestep of decreasing the first deposition-to-etch ratio to a seconddeposition-to-etch ratio further comprises increasing a rate at whichthe inert gas is flowed into the substrate processing chamber.
 14. Themethod of claim 11 wherein the step of increasing the seconddeposition-to-etch ratio to the third deposition-to-etch ratio comprisesincreasing a concentration of the deposition gas relative to aconcentration of the inert gas.
 15. The method of claim 14 wherein thedeposition gas comprises a silicon source and an oxygen source.
 16. Themethod of claim 15 wherein the inert gas comprises argon.
 17. The methodof claim 11 wherein the step of decreasing the first deposition-to-etchratio to a second deposition-to-etch ratio comprises stopping a flow ofthe deposition gas into the substrate processing chamber.
 18. The methodof claim 17 wherein the step of decreasing the first deposition-to-etchratio to a second deposition-to-etch ratio further comprises increasinga rate at which the inert gas is flowed into the substrate processingchamber.
 19. The method of claim 17 wherein the deposition gas comprisesa silicon source and an oxygen source.
 20. The method of claim 19wherein the inert gas comprises argon.
 21. The method of claim 11wherein the dielectric layer is deposited over a gap formed betweenadjacent raised surfaces, the gap having an aspect ratio of 2.5:1 orhigher.
 22. The method of claim 10 wherein the high density plasmaprocess is an inductively coupled high density plasma process.
 23. Amethod for depositing a dielectric layer over a substrate disposed in asubstrate processing chamber, the substrate having a trench formedbetween adjacent raised surfaces, the method comprising: depositing afirst portion of the dielectric layer over the substrate and within thetrench using a high density plasma process that has simultaneousdeposition and sputtering components, wherein the high density plasmadeposition process includes forming a plasma from a deposition gas andan inert gas flowed into the substrate processing chamber; thereafter,changing the flow rates of one or more of the deposition gas and inertgas to decrease a deposition-to-etch ratio of the high density plasmaprocess; and thereafter, changing the flow rates of one or more of thedeposition gas and inert gas to increase a deposition-to-etch ratio ofthe high density plasma process and deposit a second portion of thedielectric layer over the substrate.
 24. The method of claim 23 whereinthe deposition gas comprises a silicon source and an oxygen source. 25.The method of claim 24 wherein the inert gas comprises argon.
 26. Themethod of claim 24 further comprising, after the step of changing theflow rates of on or more of the deposition and inert gas to increase adeposition to etch ratio of the high density process, repeating one ormore times a sequence of (i) changing the flow rates of one or more ofthe deposition gas and inert gas to decrease a deposition-to-etch ratioof the high density plasma process and then changing the flow rates ofone or more of the deposition gas and inert gas to increase adeposition-to-etch ratio of the high density plasma process and deposita portion of the dielectric layer over the substrate.
 27. The method ofclaim 24 wherein the trench has an aspect ratio of 2.5:1 or higher. 28.The method of claim 27 wherein the trench is a via etched on adielectric layer.
 29. The method of claim 24 wherein the step ofchanging the flow rates of one or more of the deposition gas and inertgas to decrease a deposition-to-etch ratio of the high density plasmaprocess comprises terminating a flow of silicon source into thesubstrate processing chamber.
 30. The method of claim 29 wherein thestep of changing the flow rates of one or more of the deposition gas andinert gas to increase a deposition-to-etch ratio of the high densityplasma process comprises restarting a flow of silicon source into thesubstrate processing chamber.
 31. The method of claim 30 wherein thestep of changing the flow rates of one or more of the deposition gas andinert gas to decrease a deposition-to-etch ratio of the high densityplasma process further comprises reducing a flow of the oxygen sourceinto the substrate processing chamber and the step of changing the flowrates of one or more of the deposition gas and inert gas to increase adeposition-to-etch ratio of the high density plasma process furthercomprises increasing a flow of the oxygen source into the substrateprocessing chamber.
 32. The method of claim 31 wherein the step ofreducing the flow of the oxygen source comprises terminating the flow ofthe oxygen source into the chamber and the step of increasing the flowof the oxygen source comprises restarting the flow of the oxygen sourceinto the chamber.
 33. The method of claim 23 wherein the high densityplasma process is an inductively coupled high density plasma process.34. A method for depositing a dielectric layer over a substrate disposedin a substrate processing chamber, the substrate having a gap formedbetween adjacent raised surfaces, the method comprising: flowing a firstgaseous mixture comprising a silicon source, an oxygen source and aninert gas into the chamber and forming a high density plasma from thefirst gaseous mixture as part of a deposition process having adeposition-to-etch ratio; thereafter, decreasing a flow rate of at leastone of the silicon source and oxygen source while maintaining the highdensity plasma in the substrate processing chamber and decreasing thedeposition-to-etch ratio of the process; and thereafter, increasing aflow rate of at least one of the silicon source and oxygen source whilemaintaining the high density plasma in the substrate processing chamberthereby increasing the deposition-to-etch ratio of the process.
 35. Themethod of claim 34 wherein the step of decreasing the flow rate of atleast one of the silicon source and oxygen source comprises decreasingthe flow rate of both the silicon source and oxygen source and whereinthe step of increasing the flow rate of at least one of the siliconsource and oxygen source comprises increasing the flow rate of both thesilicon source and oxygen source.
 36. The method of claim 35 wherein thestep of decreasing the flow rate of at least one of the silicon sourceand oxygen source further comprises increasing a flow rate of the inertgas.
 37. The method of claim 36 wherein the step of increasing the flowrate of at least one of the silicon source and oxygen source furthercomprises decreasing a flow rate of the inert gas.
 38. The method ofclaim 34 wherein the silicon source is silane (SiH₄).
 39. The method ofclaim 38 wherein the oxygen source is molecular oxygen (O₂).
 40. Themethod of claim 38 wherein the inert gas is argon.
 41. The method ofclaim 34 wherein the gap has an aspect ratio of 2.5:1 or higher.
 42. Themethod of claim 34 wherein forming the high density plasma comprisesforming an inductively coupled high density plasma.
 43. A method fordepositing a dielectric layer over a substrate disposed in a substrateprocessing chamber, the substrate having a gap formed between adjacentraised surfaces, the method comprising: flowing a first gaseous mixturecomprising a silicon source, an oxygen source and an inert gas into thechamber and forming a high density plasma from the first gaseous mixtureto deposit a first portion of the dielectric layer over the substrate ina deposition process having a first deposition-to-etch ratio;thereafter, terminating a flow of the silicon source into the chamberwhile maintaining the high density plasma and decreasing adeposition-to-etch ratio of the process; and thereafter, reintroducing aflow of the silicon source into the chamber while maintaining the highdensity plasma and increasing a deposition-to-etch ratio of the processto deposit a second portion of the dielectric layer over the substrate.44. The method of claim 43 wherein the step of terminating the flow rateof the silicon source further comprises increasing a flow rate of theinert gas into the chamber and the step of reintroducing a flow of thesilicon source further comprises decreasing the flow rate of the inertgas into the chamber.
 45. The method of claim 43 wherein the step ofterminating the flow of the oxygen source further comprises terminatinga flow of the oxygen source into the chamber and the step ofreintroducing a flow of the silicon source further comprisesreintroducing the flow of the oxygen source into the chamber.
 46. Themethod of claim 45 wherein the step of terminating the flow rate of thesilicon source further comprises increasing a flow rate of the inert gasinto the chamber and the step of reintroducing a flow of the siliconsource further comprises decreasing the flow rate of the inert gas intothe chamber.
 47. The method of claim 46 wherein the silicon source issilane (SiH₄).
 48. The method of claim 47 wherein the oxygen source ismolecular oxygen (O₂).
 49. The method of claim 48 wherein the inert gasis argon.
 50. The method of claim 48 wherein the gap has an aspect ratioof 2.5:1 or higher.
 51. The method of claim 43 wherein forming the highdensity plasma comprises forming an inductively coupled high densityplasma.